The British government has joined press freedom advocates and journalists in expressing dismay and disgust with Donald Trump’s remarks at a rally, where he praised the unprovoked assault on a Guardian US journalist by the state’s congressman, Greg Gianforte.

At the Republican rally in Montana on Thursday night, the president lauded and made jokes about the violent attack by Gianforte, when he was a candidate, on the Guardian’s political reporter Ben Jacobs in 2017.

A spokeswoman for the British prime minister, Theresa May, when asked about the president’s remarks, said on Friday: “Any violence or intimidation against a journalist is completely unacceptable.”

Journalists across the US launched into fierce criticism of the congressman, via social media.

“Gianforte is a criminal. He pled guilty to [assault]. The president is congratulating a criminal on committing a crime,” said the New York Times correspondent Binyamin Appelbaum on Twitter.

Trump’s comments “mark the first time the president has openly and directly praised a violent act against a journalist on American soil,” added the New York Times reporter Sheryl Gay Stolberg.

Trump fondly reminisced about the physical assault that occurred on 24 May last year when Jacobs, the Guardian’s political correspondent, asked Gianforte a question about healthcare policy in the course of a special congressional election in Montana. At Thursday’s rally, Trump said that anyone who could perform a body-slam, as Gianforte did on Jacobs, was “my guy”, and that news of the attack, which occurred the night before the special election, probably helped Gianforte win.

Trump finished his account of the physical assault by saying of Gianforte: “He’s a great guy. Tough cookie.” The partisan crowd at the rally in Missoula in western Montana clapped and cheered.

On Friday afternoon, on his way to a rally in Arizona, Trump was asked if he regretted the comments. He said: “No, no, no, not at all,” according to a tweet from a CNN reporter traveling with the president. He labelled the rally a tremendous success and called Gianforte a “tremendous person”.

The writers’ organization PEN America, which had filed a lawsuit earlier this week against Donald Trump accusing him of violating the first amendment of the US constitution by using his powerful position to threaten press freedom, has also condemned the president’s encouragement for Gianforte’s attack.

In a statement issued on Friday, PEN America said Trump’s “explicit praise” for Gianforte’s assault “marks a startling new low in terms of the White House’s open hostility toward the press”.

It added: “Trump’s remarks are a chilling reminder that US global leadership on press freedom has collapsed utterly under the president’s watch. In its place is an attitude of contempt, excusing and now even applauding violence toward the press.”

The world’s press would welcome a statement from the US government that it is committed to the rights of journalists everywhere

Katharine Viner

Katharine Viner, the editor-in-chief of the Guardian, said on Friday: “At a time when reporters around the world are being harassed, arrested and even murdered these are incredibly irresponsible comments, which fly in the face of press freedom and send a dangerous message to autocrats and dictators around the world.”

She added: “The world’s press would welcome a clear statement from the US government that it remains committed to the rights of journalists everywhere to do their work without fear of violence or repression.”

The CNN reporter Jim Acosta, who was at the rally in Montana, observed: “The disturbing part of Trump’s jokes about Gianforte was the effect on the crowd. I saw one young man in the crowd making body-slam gestures. He looked at me and ran his thumb across his throat. I talked to him after the rally was over. He couldn’t stop laughing.”

A number of journalists pointed out how Trump’s comments are especially troubling this week, coming as evidence mounts that the Saudi Arabian crown prince, Mohammed bin Salman, is directly linked to the presumed murder of journalist and Saudi critic Jamal Khashoggi in Istanbul earlier this month.

“Tonight [Trump] celebrates an assault on a reporter in Montana at the same time as his Administration tries to minimize the murder of a reporter in Turkey. His words matter, and they reveal his character,” said the New Yorker and CNN contributor Jeffrey Toobin.

The Washington Post executive editor, Marty Baron, referenced a statement issued by the Guardian US editor, John Mulholland, on Thursday night soon after the event, noting that the president’s remarks run “the risk of inviting other assaults on journalists both here and across the world”.

Mulholland’s statement continued: “We hope decent people will denounce these comments and that the president will see fit to apologize for them.”

On Friday the White House Correspondents’ Association president, Olivier Knox, said: “All Americans should recoil from the president’s praise for a violent assault on a reporter doing his constitutionally protected job. This amounts to the celebration of a crime by someone sworn to uphold our laws and an attack on the first amendment by someone who has solemnly pledged to defend it.”

Meanwhile, the president’s son, Eric Trump, defended his father’s comments during an appearance on Fox News. When asked to address the controversy Eric Trump told the host: “Oh, stop. He wasn’t the guy who body-slammed anyone. He can have fun.”

In an appearance on CNN’s Anderson Cooper 360 on Friday evening, Jacobs spoke for the first time about hearing the president praise his assault in front of the Montana crowd: “It’s mind-boggling and it’s still a little bit tough to wrap my head around.”

He added: “A tough cookie doesn’t attack someone out of nowhere, without provocation, for asking a question about healthcare policy.”

Asked by Cooper if he would like an apology from Trump, Jacobs replied: “My concern is not about my situation as much as it is with Jamal Khashoggi … [and] the signal this sends about how the United States and how the president of the United States views journalists.”